Contact activation in vitro. (A) Filtration with Minisart filters does not cause significant contact activation: FXIIa generation was measured before (control) and after filtration of plasma with the filters used in our Blood paper,1 and kaolin (100 μg/mL) was used as positive control (n = 4, ns, nonsignificant Student t test). (B) Amelung KC4 causes contact activation, leading to substantial thrombin generation: pooled citrated plasma samples with or without CTI corn trypsin inhibitor (CTI) were incubated for 20 minutes at 37°C in Amelung KC4, ReoRox4, or polypropylene (PP) tubes. FXIIa generation was measured as described previously1 with the fluorescent substrate present during incubation in the instrument. Bars represent FXIIa substrate fluorescence as percentage of the PP tubes (n = 8, background fluorescence of inhibitor/vehicle additions were compensated). Aliquots from incubated plasma were used for subsequent real-time thrombin generation measurements in the presence of 10 μM phospholipids. Curves represent means of 4 independent experiments.
